Add support for ErrorKind and RetryKind to all error models (#180)

* Modeling Structured Retries

* Improvements to docs

Co-authored-by: David Barsky <dbarsky@amazon.com>

* Improve RetryKind documentation

* Remove println, add .

* Rename to classify

* Add RetryPolicy test

* Fix clippy errors

* Remove unused paramaterization of AwsRetryPolicy

* Add missing retry module

* Cut down on generated code

* Fix tests

* Rename error_kind to retryable_error_kind

* Fix tests

Co-authored-by: David Barsky <dbarsky@amazon.com>